Inputs of Phosphorus to Aquatic Systems from Machine Dishwashing Detergents: An Analysis of Measured and Potential Loading

Four lines of investigation appear to converge on the same conclusion: Phosphorus inputs to lakes and streams in Massachusetts and Vermont from machine dishwashing detergent comprise a very small portion of the total load to those systems. Analysis of stream data from two intensive studies in Massachusetts, a phosphorus loading analysis for Lake Champlain in Vermont, assessment of the itemized loads to multiple New England lakes, and extrapolation of wastewater treatment facility responses to the reduction of phosphorus in laundry detergents all indicate that there are very limited contributions of phosphorus from dishwashing detergent sources and minimal potential to realize any significant reduction in loading from a ban on P in machine dishwashing detergent.

Overall, reductions in phosphorus achievable through restrictions in the amount of P in machine dishwashing detergents will not meaningfully reduce P concentrations and associated algal levels in Massachusetts or Vermont waters. The greatest reduction in P loading through restriction of P content of machine dishwashing detergent is associated with aquatic systems that are strongly influenced by WWTF discharges subjected to no active P removal. Such systems are rare in New England, and even with such restrictions these heavily impacted waters will fall far short of achieving water quality goals.

The range of P contribution from machine detergent for the cases analyzed in this report was 0.2 to 10% of total P load, with an estimated possible maximum of 17% for systems dominated by WWTFs practicing only primary treatment with no addition of chemicals for P removal. The potential for reducing the P load through restriction of P content of machine dishwashing detergent is limited to 0 to 7% in the cases studied, with estimates >2% associated with high loading from WWTFs applying no active P removal. Again, such systems are rare in New England and would not be detectably improved by reductions in machine dishwashing detergent P content. Load reductions of <2% that might be achieved by a machine dishwashing detergent P ban in areas served by septic systems or WWTFs with active P removal would also not result in any significant reduction in P load or concentration in the associated aquatic system.

Eutrophication in Chesapeake Bay Before and After Implementation of Maryland`s Phosphate Detergent Ban

A statewide phosphate detergent ban went into effect ln Maryland on December 1, 1985. Similar legislation became effective in the District of Columbia in September of 1986. Projected benefits included improvements in the quality of Chesapeake Bay waters due to reductions in phosphorus loadings from municipal discharges without phosphorus removal facilities. Limited data indicate that phosphorus concentrations in sewage discharged from the Maryland treatment plants without phosphorus removal facilities decreased an average of 33%. However, direct relationships between phosphorus loading and biological responses in the Bay, as measured by peak algal densities or by the depletion of dissolved oxygen from bottom waters, cannot be presumed because these responses are controlled by many factors including phosphorus, nitrogen, light temperature, and hydrodynamic features. This report describes eutrophication related water quality conditions in the Bay, its estuaries, and its tributaries before and after implementation of the phosphate detergent bans, based upon analysis of monitoring data collected between mid 1984 and mid 1987.

Analyses of river monitoring data indicate that reductions in phosphorus loadings to the Bay resulting from the phosphate detergent ban are similar to projections made prior to the ban`s implementation. Other factors, including municipal phosphorus removal, reduced phosphorus loads further during the study period. However, corresponding decreases in algal productivity were not detected at Bay or estuary stations. While this result could reflect algal changes that were too small to detect, the lack of algal response is clearly consistent with observations made in this report and by others that factors other than phosphorus, particularly nitrogen, regulate algal growth and related water quality conditions.

The full range of costs and benefits must be considered in evaluating the phosphate detergent ban and in comparing it with alternative strategies for achieving the same management objectives. Considering the small changes in phosphorus loading resulting from the ban and the importance of limiting nutrients other than phosphorus, it is clear that the ban in itself contributes 1ittle to the cause of restoring the Bay.

Phosphorus Loads to the Chesapeake Bay System

The phosphorus loads from the publicly owned treatment works (POTWs) or municipal wastewater treatment plants in the Chesapeake Bay basin can be estimated based on existing data and information. However, not all these phosphorus loads will reach the tidal system of the Bay and the Bay proper after they are released from the POTWs. A portion of the municipal phosphorus loads in the upper sub-basins of major tributaries will be lost before it reaches the fall line. That is, one pound of phosphorus which enters the free-flowing river is subject to in-stream processes (e.g., settling, algal uptake, mineralization, dilution, etc.) which result in a reduced load arriving at the fall line than originally entered the river.

The purpose of this study is to quantify the POTW phosphorus loads entering the Bay. Three major river basins (Susquehanna, Potomac and James) were selected for the study.

Chemical Treatment and Enhanced Biological Removal of Phosphates at Wastewater Treatment Plants

The report presents a literature review and cost analysis of chemical treatment processes and enhanced biological and biological-chemical removal of phosphorus.

A Multiple Lake Method to Analyze Temporal Variations

The Soap and Detergent Association initiated a lake monitoring survey from 1978 through 1983 to ascertain the effectiveness of an interim detergent phosphorus ban in the state of Wisconsin. A paired-lake approach was employed in this study. Lakes expected to be impacted by wastewater effluent nutrient loadings were monitored along with lakes not impacted by effluent. Physical, chemical and biological parameters were recorded. The ensuing statistical analysis has based comparisons between geographically proximate lake pairs, one representing an effluent impacted lake and one not. Initial work has focused upon the use of a linear model to determine whether a time-dependent change in either total phosphorus or chrorophyll-a concentration or Secchi depth could be determined between the lake pairs.

Biological parameters included algal cell concentrations enumerated by algal division. This report applies linear modeling technique to these parameters and also investigates the data requirements which would be necessary in order to increase the occurrence of determining a change associated with imposition of the detergent phosphorus ban.